McDougal Littell Science
Cells and Heredity

The microscope led to the discovery of cells.

READING TiP

The word microscopic is an
adjective made from the
noun microscope. Things
that are microscopic are too
small to see without the use
of a microscope.

Most cells are microscopic, too small to see without the aid of a
microscope. A microscope is an instrument which makes an object
appear bigger than it is. It took the invention of this relatively simple
tool to lead to the discovery of cells. In the 1660s, Robert Hooke
began using microscopes to look at all sorts of materials. Anton van
Leeuwenhoek took up similar work in the 1670s. They were among
the first people to describe cells.

Hooke's Drawing of Cells

Robert Hooke published this drawing
of dead cork cells in 1665. The
microscope he used, shown at left,
has two lenses.

Robert Hooke gave the cell its
name. While looking at a sample
of cork, a layer of bark taken from
an oak tree, he saw a group of
similarly shaped compartments
that looked to him like tiny empty
rooms, or cells. You can see from
his drawing, shown at right, how
well these cells fit Hooke's description.
Hooke used a microscope
that magnified objects 30 times
(30×). In other words, objects
appeared thirty times larger than
their actual size.

The bark cells Hooke saw were
actually dead cells, which is why they appeared empty. Anton van
Leeuwenhoek was one of the first people to describe living cells.
He looked at a drop of pond water under a microscope. Imagine his
surprise when he saw that a drop of water was full of living things!
Using lenses that could magnify an object almost 300×, he observed
tiny unicellular organisms like those shown on page 11.

CHECK YOUR READiNG

How did the invention of the microscope change the study
of biology?

You can understand how powerful a microscope is if you think
of how big a penny would be if it were increased in size 30×. It
would be a little bigger than the tire of a ten-speed bicycle. Enlarged
300×, that penny would be so big that you would need a tractortrailer
to move it. Magnify your best friend 30× (supposing a height
of 1.5 meters, or almost 5 ft), and your friend would appear to be 45
meters (147 ft) tall. That's almost the height of Niagara Falls. Change
the magnification to 300×, and your friend would appear to be 450
meters (1470 ft) tall—taller than the Empire State Building.